Rational Application of Angular Contact Ball Bearing in Electric Spindle

The angular contact ball bearing often runs at high speed in the electric spindle, so the centrifugal force has a great influence on the running state of the bearing. In the static state, the contact points between the steel ball and the inner and outer rings are A and B respectively At high speed, the centrifugal force tends to make the steel ball move outward, that is, A. Move to A1 B0 and move to B1. At this time, the contact angle of the inner ring will increase and the contact angle of the outer ring will decrease. As a result, the steel ball centroid deviates from the rotation axis, generating gyro torque. The steel ball will slip to a certain extent while rolling. The friction heat generated by sliding will not only aggravate the temperature rise of the bearing, but also lead to local annealing of the steel ball surface, increasing wear and burn. In order to overcome the influence of centrifugal force, angular contact ball bearings always run with preload in the spindle. Proper preload can keep the contact angle of inner and outer rings during operation, which can not only prolong the service life of bearings, but also improve the rigidity of bearings and spindles.

If the preload is too large, the bearing lubrication and heat dissipation conditions are poor. Under the same service conditions, the bearing has a short life, is easy to burn or get stuck, and the high-speed performance is worse, but the support rigidity of the bearing and main shaft is greatly increased. If the preload is too small, the overall rigidity and bearing capacity of the main shaft will decrease significantly. If the preload value is not enough to overcome the influence of the axial force and driving force on the spindle, the spindle will produce obvious vibration during operation, and obvious vibration marks will appear on the machined workpiece surface. If the preload is not enough to suppress the gyroscopic torque, the spindle bearing will rapidly heat up due to "slipping" during operation, and the steel ball surface has obvious "cat's eye" wear marks.

There are three kinds of preload values of light, medium and heavy on the bearing samples of Dalian Redmei. However, when it is used in the electric spindle, it should be considered comprehensively according to the load condition, lubricating oil and cooling mode. The selection principle is that the preload should be as close as possible to the actual application needs, and the influence of external loads on the preload should be considered.

The reasonable support of the electric spindle is two groups of bearing groups. Considering the assembly process, the front bearing group is fixed. For single set and series bearing groups, the spring group exerts preload by pushing forward and pulling back. For parallel bearing, if it is not paired (use constant height pad) The preload shall be adjusted by the height difference between the inner and outer pads. When selecting the main shaft support, the series type (DT) is used for the occasions with large unidirectional axial force. The DB parallel type can bear two-way loads and is used for the occasions with accurate axial positioning, such as the main shaft for grinding the groove of the bearing ring. DF parallel type can be used for multi-point support or when the concentricity of the front and rear seat holes of the bearing is difficult to guarantee.